add-padding.lua

-- Aseprite Script: Add 1px Padding to Tilemap
-- Takes a tilemap and creates a new file with 2x larger grid (1px padding per tile)

local sprite = app.activeSprite
if not sprite then
  app.alert("No active sprite")
  return
end

-- Get original sprite properties
local origWidth = sprite.width
local origHeight = sprite.height
local origGrid = sprite.gridBounds
local gridWidth = origGrid.width
local gridHeight = origGrid.height

-- Check if grid is defined
if gridWidth <= 0 or gridHeight <= 0 then
  app.alert("No grid defined in the original sprite")
  return
end

-- Calculate number of tiles
local tilesX = math.floor(origWidth / gridWidth)
local tilesY = math.floor(origHeight / gridHeight)

-- Calculate new dimensions with padding
local newGridWidth = gridWidth + 2
local newGridHeight = gridHeight + 2
local newWidth = tilesX * newGridWidth
local newHeight = tilesY * newGridHeight

-- Create new sprite
local newSprite = Sprite(newWidth, newHeight, sprite.colorMode)
newSprite.gridBounds = Rectangle(0, 0, newGridWidth, newGridHeight)

-- Copy palette
newSprite:setPalette(sprite.palettes[1])

-- Delete the default layer in new sprite
if #newSprite.layers > 0 then
  newSprite:deleteLayer(newSprite.layers[1])
end

-- Process each layer
for i, layer in ipairs(sprite.layers) do
  if layer.isImage then
    -- Create corresponding layer in new sprite
    local newLayer = newSprite:newLayer()
    newLayer.name = layer.name
    newLayer.opacity = layer.opacity
    newLayer.blendMode = layer.blendMode

    -- Get the cel from frame 1
    local cel = layer:cel(1)
    if cel then
      local image = cel.image
      local celPos = cel.position
      local newImage = Image(newWidth, newHeight, sprite.colorMode)

      -- Copy tiles with padding
      for ty = 0, tilesY - 1 do
        for tx = 0, tilesX - 1 do
          -- Source position in original sprite coordinates
          local srcX = tx * gridWidth
          local srcY = ty * gridHeight

          -- Convert to image coordinates (account for cel position)
          local imgX = srcX - celPos.x
          local imgY = srcY - celPos.y

          -- Destination position in new image (with 1px padding offset)
          local dstX = tx * newGridWidth + 1
          local dstY = ty * newGridHeight + 1

          -- Copy the tile
          for y = 0, gridHeight - 1 do
            for x = 0, gridWidth - 1 do
              -- Check bounds to avoid reading outside image
              if imgX + x >= 0 and imgX + x < image.width and
                 imgY + y >= 0 and imgY + y < image.height then
                local pixel = image:getPixel(imgX + x, imgY + y)
                newImage:putPixel(dstX + x, dstY + y, pixel)
              end
            end
          end
        end
      end

      -- Create cel in new sprite at origin
      newSprite:newCel(newLayer, 1, newImage, Point(0, 0))
    end
  end
end

-- Refresh to show the new sprite
app.refresh()